Supercritical carbon dioxide thickener, method for preparing the same, and use thereof

Abstract

The application relates to the technical field of oil field chemistry, and is a supercritical carbon dioxide thickener as well as a preparation method and application thereof. The preparation of the supercritical carbon dioxide thickener comprises the following steps: adding vinyl acetate and a long-chain alpha-olefin into a solvent, mixing to obtain a monomer mixed solution; adding an initiator into the monomer mixed solution, stirring and reacting under the protection of inert gas to obtain a reaction mixed solution; after the reaction mixed solution is cooled, a terminating agent is added; and after the reaction product is subjected to alcohol precipitation, washing and drying, the supercritical carbon dioxide thickener is obtained. The supercritical carbon dioxide thickener has the characteristics of high solubility, high thickening property and environmental friendliness, can significantly improve the viscosity of carbon dioxide, and is suitable for shale oil fracturing, carbon dioxide storage and other fields.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a supercritical carbon dioxide thickener, its preparation method, and its application. Background Technology

[0002] Supercritical carbon dioxide (SCCO) has broad application prospects in unconventional oil and gas production enhancement due to its unique physical properties (such as low viscosity and high diffusivity). However, the inherent defects of SCCO severely restrict its large-scale application: its extremely low viscosity (0.03 to 0.1 mPa·s) leads to insufficient proppant carrying capacity during fracturing, rapid proppant accumulation in the near-wellbore zone, and insufficient support at the distal end of the fracture; its high diffusivity (10⁻⁶ mPa·s) also hinders its large-scale application. -7 m 2 The carbon dioxide escape rate (CO2 / s) forms a gas cap beneath the caprock, inducing storage failure risks (field monitoring shows a CO2 escape rate as high as 15% to 30%). The high miscibility pressure with crude oil (>20 MPa) makes effective displacement difficult in low-permeability reservoirs. To mitigate CO2 diffusion and increase residual CO2 sequestration, methods such as water-gas alternating injection, carbonated water injection, CO2 foaming, and CO2 thickening have been proposed in recent years. For the injection of large amounts of water and surfactant solutions, as well as the adsorption of surfactants on the rock surface, CO2 thickening can effectively suppress CO2 diffusion and enhance storage safety.

[0003] Carbon dioxide thickeners, by significantly improving the viscosity and stability of supercritical carbon dioxide, can effectively solve the problems of weak sand-carrying capacity and severe filtration loss in traditional fracturing fluids. The ideal carbon dioxide thickener criteria mainly include the following aspects: good solubility in carbon dioxide, excellent carbon dioxide thickening effect, and environmental friendliness. Existing carbon dioxide thickeners mainly include polymers, surfactants, small molecule compounds, and nanoparticles, among which polymer thickeners have been the most extensively studied, accounting for more than half of all research, and are also considered the most successful carbon dioxide thickeners. The types of polymer-based carbon dioxide thickeners reported in the literature include fluorinated polymers, siloxane polymers, hydrocarbon polymers, and oxygen-containing hydrocarbon polymers. For example, Chinese patent document CN107236091A discloses a supercritical carbon dioxide thickener, its preparation method, and its application. This thickener contains the following components: (a) polydimethylsiloxane; (b) acrylate compounds; (c) styrene compounds; (d) an initiator; and (e) an emulsifier; wherein component (a) is polydimethylsiloxane with a viscosity of 50 to 3000 mPa·s. Chinese patent document CN112341567A discloses a supercritical carbon dioxide thickener for oil displacement, its preparation method, and its application. This thickener is synthesized by free-base polymerization using fluorinated acrylates, tertiary amine acrylates, and styrene as monomers.

[0004] Despite extensive research in this field, the development of polymer thickeners still faces several challenges. First, the solubility of polymer thickeners in supercritical carbon dioxide is highly dependent on their molecular structure; most high-molecular-weight polymers struggle to achieve ideal solubility in this environment. Second, molecular weight is directly related to thickening efficiency; excessively large molecular weights result in a sharp drop in solubility, while excessively small molecular weights lead to low thickening efficiency. Furthermore, temperature significantly affects the thickening effect; in high-temperature environments (>50°C), the thickening rate of most existing thickeners decreases by more than 50%, making it difficult to maintain stable viscosity in practical engineering applications. Therefore, further research into the thickening mechanism of polymers in supercritical carbon dioxide is urgently needed to develop efficient and environmentally friendly supercritical carbon dioxide thickeners. Summary of the Invention

[0005] This invention provides a supercritical carbon dioxide thickener and its preparation method, which overcomes the shortcomings of the prior art and can effectively solve the problems of poor solubility and high temperature sensitivity of existing supercritical carbon dioxide thickeners.

[0006] One of the technical solutions of this invention is achieved through the following measures: a method for preparing a supercritical carbon dioxide thickener, comprising the following steps: Step 1: Add vinyl acetate and long-chain α-olefin to a solvent and mix to obtain a monomer mixture; Step 2: Add an initiator to the monomer mixture and stir the mixture under an inert gas atmosphere to obtain a reaction mixture. Step 3: After the reaction mixture is cooled, a terminator is added. The reaction product is then subjected to alcohol precipitation, washing, and drying to obtain a supercritical carbon dioxide thickener.

[0007] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The molecular weight of the aforementioned supercritical carbon dioxide thickener is 50 kDa to 150 kDa.

[0008] The structural formula of the above long-chain α-olefin is CH2=CH-(CH2). n CH3, where n = 9 to 15.

[0009] The molar ratio of the above vinyl acetate to long-chain α-olefin is 1:1 to 1:3.

[0010] The solvent mentioned above is toluene.

[0011] The initiator mentioned above is benzoyl peroxide, and the amount of initiator used is 0.5% to 1% of the total mass of vinyl acetate and long-chain α-olefin.

[0012] The terminator is hydroquinone, and the amount of terminator used is 0.1% to 0.3% of the total mass of vinyl acetate and long-chain α-olefin.

[0013] In step two above, the reaction temperature is 60℃ to 80℃, and the reaction time is 4h to 8h.

[0014] In step three above, the temperature is lowered to 30°C to 40°C.

[0015] The second technical solution of the present invention is achieved through the following measures: a supercritical carbon dioxide thickener prepared by a method for preparing a supercritical carbon dioxide thickener.

[0016] The third technical solution of the present invention is achieved through the following measures: the application of a supercritical carbon dioxide thickener in supercritical carbon dioxide fracturing fluid.

[0017] The following are further optimizations and / or improvements to the third technical solution of the above invention: The mass concentration of the aforementioned supercritical carbon dioxide thickener in supercritical carbon dioxide fracturing fluid is 1% to 3%.

[0018] This invention provides a supercritical carbon dioxide thickener and its preparation method. This supercritical carbon dioxide thickener features high solubility, high thickening power, and environmental friendliness, and can significantly improve the viscosity of carbon dioxide, making it suitable for applications such as oil and gas fracturing. Detailed Implementation

[0019] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solution of this invention and the actual situation. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; room temperature in this invention generally refers to a temperature between 15°C and 25°C, and is generally defined as 25°C.

[0020] The present invention will be further described below with reference to embodiments: Example 1: The preparation method of this supercritical carbon dioxide thickener includes the following steps: Step 1: Add vinyl acetate and long-chain α-olefin to a solvent and mix to obtain a monomer mixture; Step 2: Add an initiator to the monomer mixture and stir the mixture under an inert gas atmosphere to obtain a reaction mixture. Step 3: After the reaction mixture is cooled, a terminator is added. The reaction product is then subjected to alcohol precipitation, washing, and drying to obtain a supercritical carbon dioxide thickener.

[0021] Example 2: As an optimization of the above example, the molecular weight of the supercritical carbon dioxide thickener is 50kDa to 150kDa.

[0022] Example 3: As an optimization of the above examples, the structural formula of the long-chain α-olefin is CH2=CH-(CH2). n CH3, where n = 9 to 15.

[0023] Example 4: As an optimization of the above examples, the molar ratio of vinyl acetate to long-chain α-olefin is 1:1 to 1:3.

[0024] Example 5: As an optimization of the above examples, the solvent is toluene.

[0025] Example 6: As an optimization of the above example, the initiator is benzoyl peroxide, and the amount of initiator is 0.5% to 1% of the total mass of vinyl acetate and long-chain α-olefin.

[0026] Example 7: As an optimization of the above examples, the terminator is hydroquinone, and the amount of terminator is 0.1% to 0.3% of the total mass of vinyl acetate and long-chain α-olefin.

[0027] Example 8: As an optimization of the above example, in step two, the reaction temperature is 60°C to 80°C and the reaction time is 4h to 8h.

[0028] Example 9: As an optimization of the above example, in step three, the temperature is lowered to 30°C to 40°C.

[0029] The polymerization reaction of vinyl acetate and long-chain α-olefins in this invention can be represented as follows: .

[0030] Example 10: Application of the supercritical carbon dioxide thickener in supercritical carbon dioxide oil displacement agent; the mass concentration of the supercritical carbon dioxide thickener in supercritical carbon dioxide fracturing fluid is 1% to 3%.

[0031] Example 11: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-dodecene were weighed in a molar ratio of 1:2 and added to toluene solvent. Benzoyl peroxide (0.5% of the total mass of vinyl acetate and 1-dodecene) was then added. The mixture was stirred at 80°C and 800 rpm for 6 hours under nitrogen protection to obtain a reaction mixture. After the reaction mixture was cooled to 40°C, hydroquinone (0.1% of the total mass of vinyl acetate and 1-dodecene) was added to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0032] Example 12: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-dodecene were weighed in a molar ratio of 1:1 and added to toluene solvent. Benzoyl peroxide was added at 1% of the total mass of vinyl acetate and 1-dodecene. The mixture was stirred at 60°C and 800 rpm for 8 hours under nitrogen protection to obtain a reaction mixture. After the reaction mixture was cooled to 35°C, hydroquinone was added at 0.1% of the total mass of vinyl acetate and 1-dodecene to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0033] Example 13: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-dodecene were weighed in a molar ratio of 1:3 and added to toluene solvent. Benzoyl peroxide was added at 0.8% of the total mass of vinyl acetate and 1-dodecene. The mixture was stirred at 70°C and 800 rpm for 5 hours under nitrogen protection to obtain a reaction mixture. After the reaction mixture was cooled to 40°C, hydroquinone was added at 0.2% of the total mass of vinyl acetate and 1-dodecene to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0034] Example 14: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-tetradecene were weighed at a molar ratio of 1:2.5 and added to toluene solvent. Benzoyl peroxide (0.7% of the total mass of vinyl acetate and 1-tetradecene) was then added. The mixture was stirred at 65°C and 800 rpm for 6 hours under nitrogen protection to obtain a reaction mixture. After the reaction mixture was cooled to 40°C, hydroquinone (0.3% of the total mass of vinyl acetate and 1-dodecene) was added to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0035] Example 15: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-hexadecene were weighed at a molar ratio of 1:1.5 and added to toluene solvent. Benzoyl peroxide was added at 0.8% of the total mass of vinyl acetate and 1-hexadecene. The mixture was stirred at 75°C and 800 rpm for 6 hours under nitrogen protection to obtain a reaction mixture. After the reaction mixture was cooled to 30°C, hydroquinone was added at 0.2% of the total mass of vinyl acetate and 1-dodecene to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0036] Example 16: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-octadecene were weighed in a molar ratio of 1:2 and added to toluene solvent. Benzoyl peroxide was added at 1% of the total mass of vinyl acetate and 1-octadecene. The mixture was stirred at 70°C and 800 rpm for 6 hours under nitrogen protection to obtain a reaction mixture. After the reaction mixture was cooled to 40°C, hydroquinone was added at 0.3% of the total mass of vinyl acetate and 1-dodecene to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0037] Example 17: This supercritical carbon dioxide thickener was prepared according to the following steps: Vinyl acetate and 1-octadecene were weighed in a molar ratio of 1:2 and added to toluene solvent. Benzoyl peroxide (0.5% of the total mass of vinyl acetate and 1-octadecene) was then added. Under nitrogen protection, the mixture was stirred at 80°C and 800 rpm for 6 hours to obtain a reaction mixture. After the reaction mixture was cooled to 40°C, hydroquinone (0.3% of the total mass of vinyl acetate and 1-dodecene) was added to terminate the reaction. The reaction product was precipitated with alcohol, filtered, washed with anhydrous ethanol and deionized water, and dried under vacuum to obtain a supercritical carbon dioxide thickener.

[0038] Comparative Example 1: The difference from Example 12 is that 1-undecene is used instead of 1-dodecene.

[0039] Comparative Example 2: The difference from Example 17 is that 1-nonadene is used instead of 1-octadecene.

[0040] Test Example: Solubility, Thickening and Temperature Resistance Test Using a supercritical carbon dioxide pressurization system and a high-temperature, high-pressure, visual reactor, the solubility of the thickeners prepared in Examples 11 to 17 and Comparative Examples 1 and 2 in supercritical carbon dioxide under supercritical temperature and pressure conditions was tested. The dissolution state of the samples was observed, as well as the solubility at 170 s⁻¹. -1 The viscosity of supercritical carbon dioxide after 30 minutes of shearing was determined using the following steps: After filling the carbon dioxide storage tank, pressurize it to convert it into supercritical carbon dioxide for later use. Add the thickeners prepared in Examples 11-17 and Comparative Examples 1 and 2, respectively, at 2% of the amount of supercritical carbon dioxide used for testing, to a stirred tank, and seal the stirred tank. Introduce supercritical carbon dioxide into the stirred tank, filling it to the preset liquid volume. Start stirring and stir at a high speed of 1000 r / min for a certain period of time to dissolve the thickener. Stop stirring and observe the appearance and static stability of the dispersed and dissolved thickener through a viewing window. Introduce the dissolved dry fracturing fluid into the rheometer measuring cylinder. The test was conducted at a temperature of 40℃, a pressure of 15 MPa, and a shear rate of 170 s⁻¹. -1 After stabilizing under shear for 30 minutes, the dissolution time and viscosity test results were recorded. The temperature was changed to 60℃ and the pressure to 20MPa, and the viscosity properties under high temperature and high pressure were measured. The test results are shown in Table 1.

[0041] Table 1 .

[0042] The solubility test results show that the supercritical carbon dioxide thickeners of the present invention can all dissolve completely within 2 minutes, indicating that they have good wettability and dispersibility in supercritical carbon dioxide, and there is no obvious agglomeration or precipitation phenomenon in the macroscopic system. In contrast, the thickener of Comparative Example 2 did not completely dissolve even after stirring for more than 3 minutes. The thickening performance test results show that the supercritical carbon dioxide thickeners of the present invention significantly improve the viscosity of supercritical carbon dioxide, increasing it from 0.05 mPa·s to 4.20 mPa·s, an increase of 83 times, while the viscosity of the thickener in Comparative Example 1 only increased to 1.03 mPa·s. The temperature resistance test results show that although the viscosity of the supercritical carbon dioxide thickeners of the present invention decreases, the reduction is controlled within 25%, exhibiting good temperature resistance.

[0043] In summary, this invention provides a supercritical carbon dioxide thickener that can efficiently thicken supercritical carbon dioxide at a low concentration, exhibits high solubility and high thickening properties, and has a simple synthesis method, mild conditions, is environmentally friendly, and is easy to industrialize.

[0044] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for preparing a supercritical carbon dioxide thickener, characterized in that... Includes the following steps: Step 1: Add vinyl acetate and long-chain α-olefin to a solvent and mix to obtain a monomer mixture; Step 2: Add an initiator to the monomer mixture and stir the mixture under an inert gas atmosphere to obtain a reaction mixture. Step 3: After the reaction mixture is cooled, a terminator is added. The reaction product is then subjected to alcohol precipitation, washing, and drying to obtain a supercritical carbon dioxide thickener.

2. The method for preparing the supercritical carbon dioxide thickener according to claim 1, characterized in that... The molecular weight of supercritical carbon dioxide thickeners ranges from 50 kDa to 150 kDa.

3. The method for preparing the supercritical carbon dioxide thickener according to claim 1 or 2, characterized in that... The structural formula of long-chain α-olefins is CH2=CH-(CH2). n CH3, where n = 9 to 15.

4. The method for preparing the supercritical carbon dioxide thickener according to claim 1, characterized in that... The molar ratio of vinyl acetate to long-chain α-olefin is 1:1 to 1:

3.

5. The method for preparing the supercritical carbon dioxide thickener according to claim 1, characterized in that... The solvent is toluene.

6. The method for preparing the supercritical carbon dioxide thickener according to claim 5, characterized in that... The initiator is benzoyl peroxide, and the amount of initiator used is 0.5% to 1% of the total mass of vinyl acetate and long-chain α-olefins; Or / and, the terminator is hydroquinone, and the amount of terminator is 0.1% to 0.3% of the total mass of vinyl acetate and long-chain α-olefin.

7. The method for preparing the supercritical carbon dioxide thickener according to claim 1, characterized in that... In step two, the reaction temperature is 60℃ to 80℃, and the reaction time is 4h to 8h. Or / and, in step three, cool down to 30°C to 40°C.

8. A supercritical carbon dioxide thickener prepared by the method of preparing a supercritical carbon dioxide thickener according to any one of claims 1 to 7.

9. The application of the supercritical carbon dioxide thickener according to claim 8 in supercritical carbon dioxide fracturing fluid.

10. The application of the supercritical carbon dioxide thickener according to claim 9 in supercritical carbon dioxide fracturing fluid, characterized in that... The supercritical carbon dioxide thickener has a mass concentration of 1% to 3% in the supercritical carbon dioxide fracturing fluid.

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